Particle-free dockable interface for integrated circuit processing

ABSTRACT

A particle-free dockable interface is disclosed for linking together two spaces each enclosing a clean air environment. The interface is composed of interlocking doors on each space which fit together to trap particles which have accumulated from the dirty ambient environment on the outer surfaces of the doors.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 536,600 filed 9-28-83 nowU.S. Pat. No. 4,532,970, issued Aug. 6, 1985.

BACKGROUND

Processing yield has long been a major concern in integrated circuit(IC) manufacturing. A major cause of IC processing failures is theexistence of particles such as dust in the processing environment.Conventional IC processing is therefore done in a clean room in whichthe air is continuously circulated and filtered in an attempt to removethe airborne particles. In addition, personnel are usually clothed inspecial suits in an attempt to reduce the number of particles introducedas the workers move about the clean room. As a final step, many of themost vulnerable IC process steps are further contained beneath laminarflow down-drafts of filtered air to provide added protection from localsources of particulate contamination.

Unfortunately such an environment suffers from several disadvantages.First, such specially designed rooms are not only fairly expensive toconstruct and maintain, but also working in such an environment isinconvenient. Second since the size of particles which will causeproduct failure is usually equal to or greater than 1/4 to 1/3 theminimum feature size of the product, it is necessary to continuallyreduce contamination levels as dimensions are reduced in newer ICproducts in order to maintain acceptable process yields. This problembecomes especially acute as the minimum feature size drops below onemicron for very large scale integrated (VLSI) ICs.

SUMMARY

The present invention is a departure from the use of a conventionalclean room in the fabrication of ICs. Instead, a novel standardizedmechanical interface (SMIF) system is utilized that reduces particlecontamination by significantly reducing particle fluxes onto wafers.This is done by mechanically assuring that during transportation,storage, and most processing steps, the gaseous media surrounding thewafers is essentially stationary relative to the wafers, and thatparticles from exterior "ambient" environments cannot enter the waferenvironments. Experiments have shown that the SMIF system of waferhandling reduces wafer particle contamination by as much as ten timeswhen compared to conventional Class 100 clean room wafer handlingpractice. In addition, since the level of SMIF system particlecontamination is independent of the ambient external environment, ICmanufacturing can proceed in a non-clean facility. Thus, not only is theexpense and inconvenience of a clean room eliminated, but also processyields can be maintained or even improved for high density VLSIprocesses due to the lower concentration of particle contamination.

Experiments have shown that a significant number of processing defectsin VLSI circuits are caused by particles and that many of theseparticles are related to material handling by humans even iflow-particle clothing is employed. A sitting person with light hand,forearm and head movements even with proper clean-room clothing willemit more than 100,000 particles/minute, all larger than 0.3 microns.The SMIF system therefore consists of two parts: (1) a clean gas filledcanopy around the wafer handling apparatus of each piece of processingequipment; and (2) a small, clean, still-gas box to carry wafers frommachine to machine. The various pieces of the system are mechanicallyinterfaced without the need of an air-lock by means of uniqueparticle-free dockable doors which consist of a door on each piece ofequipment that fit together to trap particles which have accumulatedfrom the dirty ambient environment on the outer surfaces of the doors.Once linked together, the doors are moved as a unit into the cleaninterior space, thus opening a particle-free interface between thesystem components. Wafers are then moved through the system bymechanical arms and elevators without human intrusion. The actual wafermovement can also be fully automated through the use of robotic materialhandlers to further increase productivity. Thus by eliminating humanhandling of IC wafers and maintaining the wafers in a still-airenvironment throughout the majority of the IC process, particles arereduced and process yield is increased.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first SMIF subsystem component, a canopy, according to apreferred embodiment of the present invention.

FIGS. 2A and 2B show a second SMIF subsystem component, a cassette port,according to a preferred embodiment of the present invention.

FIGS. 3A, 3B and 3C show three versions of a third SMIF subsystemcomponent, a cassette manipulator, according to a preferred embodimentof the present invention.

FIG. 4 shows the canopy interfaced to the cassette port according to apreferred embodiment of the present invention.

FIG. 5 shows an alternative embodiment of an interface as shown in FIG.4

FIG. 6 shows a SMIF box storage unit according to a preferred embodimentof the present invention.

FIG. 7 shows a cassette storage unit according to a preferred embodimentof the present invention.

FIG. 8 shows a system interlock according to a preferred embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Conceptually, the SMIF system has two parts:

(1) a clean air canopy around the wafer handling apparatus of each pieceof processing equipment; and

(2) a small clean air box to carry wafers from machine to machine.

In practice, the SMIF system is built from several of the small cleanair boxes and canopies to form SMIF subsystems, each of which are builtfrom three SMIF subsystem components.

The first SMIF subsystem component as shown in FIG. 1 is the canopy 10.The canopy 10 is an easily removable shield that covers the waferhandling mechanisms of each piece of processing equipment 15 (e.g.,photoresist applicators, mask aligners, inspection equipment, etc.).Generally, the canopy 10 is constructed of transparent plastic such asLexan to facilitate inspection and/or maintenance within the canopy 10which may later become necessary. The other subsystem components are aSMIF cassette port 20 and a SMIF cassette manipulator 30 which arebolted onto the canopy 10 in locations that allow easy movement withinthe canopy 10. Because the canopy 10 encloses the handling mechanisms ofthe processing equipment 15, there is no need to enclose the processingequipment 15 within a clean room.

FIG. 2A shows the details of the SMIF cassette port 20. The port 20 istypically mounted on an horizontal surface 40 of the canopy 10 by meansof a canopy mounting plate 50. The port 20 further consists of a portdoor 60 and an elevator mechanism 70 that transports a cassette 80containing the IC wafers 82 into the interior of the canopy 10. Thewafers 82 are held in the cassette 80 by a wafer dampener 85 as shown inFIG. 2B which is mounted to the door 100 and is activated by the weightof the cassette 80.

A SMIF box 90, which is used for transporting cassettes 80 from onepiece of processing equipment 15 to another, interfaces with the canopy10 via the SMIF port 20. The SMIF box 90 is aligned with the SMIF port20 by means of a wedge shaped lip 95 and has a door 100 which interlockswith the door 60 on the port 20. Doors 60 and 100 together provide aparticle-free dockable interface 110, shown in FIG. 2 in the openposition, which will be described in detail shortly. The interface 110also provides means to latch the box 90 to the port 20 so that theelevator mechanism 70 can freely transport the cassette 80 between thebox 90 and the canopy 10. The doors 60 and 100 are designed so that themajority of particles on the exterior surfaces of the doors 60 and 100are trapped between the doors 60 and 100. Thus, the wafers carried inthe cassette 80 are not contaminated when the interface 110 is opened.

Once the cassette 80 is within the canopy 10, the cassette 80 can bemaneuvered as needed by the cassette manipulator 30. A manually operatedcassette manipulator 30 is shown in FIG. 3. The manipulator 30 typicallyhas an arm 120 which is 2-3 feet long and a cassette gripper 130 on theinside (clean air) end and a hand grip 140 on the outside (ambient) end.A bearing 150 provides angular and in-out movement for the arm 120 aswell as providing an air seal to prevent the intrusion of dirty ambientair. The cassette gripper 130 is actuated by gripper switch 155 to holdthe cassette 80 which can then be rotated about the vertical axis by athumb wheel 160 mounted on the hand grip 140. A manipulator mountingplate 170 supports the bearing 150 and a port actuation switch 180 whichactuates the latching of doors 60 and 100 and the movement of theelevator mechanism 70. Mechanical dampers 181 are provided along thethree axis of motion of arm 120 to limit the speed of the movement ofthe gripper 130. The manipulator mounting plate 170 is bolted to thecanopy 10 as shown in FIG. 1. Two alternatives of the cassettemanipulator 30 which are often useful are a poker 182 as shown in FIG.3B and a wafer gripper 183 as shown in FIG. 3C. The poker 182 is acassette manipulator 30 without a gripper 130 used to push objectswithin the canopy 10. The wafer gripper 183 is a cassette manipulator 30with a three-pronged claw 184 or similar mechanism replacing thecassette gripper 130 so that the wafers can be grasped directly asneeded.

It should be noted that both the canopy 10 and SMIF box 90 describedabove totally exclude humans and do not utilize constantly movingfiltered air to decrease particles on the IC wafer surfaces. Rather, ICcleanliness is achieved by maintaining a still-air interior environment.The canopy 10 and box 90 can each be equipped with particle-filteredopenings 11 and 91 respectively, (see FIG. 4) to allow continuousequalization between internal and external (ambient) air pressures. Suchfiltered pressure equalization openings 11 and 91 minimize pressuredifference and air flow between the canopy 10 and box 90 as theinterface 110 is opened and the wafers are moved from the box 90 intothe canopy 10. In addition, access to the interiors of the canopy 10 andbox 90 are by means of mechanical arms which occupy essentially constantvolume within the enclosures so that there is no significant change ininterior volume as IC wafers are moved about. Hence, since there islittle or no change of interior air pressure during processing, there isno need for air-tight seals on the canopy 10 or box 90 and particles onthe IC wafer surfaces are further decreased by inhibiting the movementof air.

FIG. 4 shows a vertically opened version of the SMIF cassette port 20. Ahorizontally opened version is also easily achieved by slight mechanicalmodifications to the vertically opened version to include a positivespring loaded latch 185 and release cable 187 as shown in FIG. 5 betweenthe doors 60 and 100 since gravity cannot be used to hold the doorstogether. The cassette box 90 is designed to contain one cassette 80 andis only slightly larger than the cassette 80 itself, which holds the ICwafers. The cassette box 90 will generally have transparent sides tofacilitate observations by humans which may be necessary. Theparticle-free dockable interface 110 mentioned earlier permits clean,particle-free access between two otherwise independent cleanenvironmental systems such as the canopy 10 and the SMIF box 90. Theinterface 110 avoids letting air-borne particles, especially those inthe size range between 0.1 to 20 microns, from entering the otherwiseclean equipment containers.

FIG. 4 shows the interconnection of the envelopes of the closed spaces10 and 90 along a contact area 190. In the present invention it isnecessary to open the contact area 190 without exposing the spaces 10and 90 to the external environment or to the previously externalsurfaces of doors 60 and 100 of spaces 10 and 90 respectively. Inparticular, when the doors 60 and 100 are opened, the portions of theexternal surfaces of the contact area 190 lying within the contactopening 195 are made to contact one another thereby trapping particleswhich may exit on the external surfaces between the doors 60 and 100.The contact area 190 is then kept in contact while the doors 60 and 100are moved as a single unit into the space 10.

The doors 60 and 100 are either circularly or rectangularly symmetricalabout axis 200. Before the interface 110 is opened, door 100 is held inplace by latches 210 which pass through the walls of spaces 90 by meansof airtight bearings or bushings 215. Spaces 10 and 90 are held togetherin lip 95 by clamp 220. In the specific embodiment shown in FIG. 4, apiston 230 of the elevator 70 is located outside of spaces 10 and 90 toconserve space within the enclosures. Piston 230 is coupled to door 60by an arm 240 and rod 250. The rod 250 passes through the wall of space10 by means of a bellows 260 which prevents the intrusion of dirtyambient air. A vent 270 is provided to allow the equalization of airpressure inside of bellows 260 as the elevator 70 moves and the bellows260 expands and contracts. Note that the air passing through vent 270 isdirty ambient air, but this does not contaminate space 10 because thebellows is sealed to the inside of space 10 and arm 250. To open theinterface 110, latches 210 are released, piston 230 is extended, and theelevator 70 transports both doors 60 and 100 as a unit into space 10,thereby carrying the cassette 80 aligned with the aid of guide lips 275into space 10 while trapping surface particles between the two doors 60and 100 and preventing the intrusion of dirty ambient air.

In order to trap surface particles between doors 60 and 100 it is onlynecessary that the doors contact each other uniformly and closely aroundtheir outer perimeters 280 and 285 respectively. The doors 60 and 100need not fit flush with each other along the entire interface 110. Infact, it is desirable that an air gap 290 inside of the outer perimeters280 and 285 be left between the doors 60 and 100. The air gap 290provides a compressive air space between the doors 60 and 100 so thatthe dirty air trapped between the doors 60 and 100 does not rush out athigh velocity in the plane perpendicular to axis 200 as the doors 60 and100 are brought together, thereby potentially sweeping part of the dirtytrapped air into spaces 10 or 90. The air gap 290 also prevents doors 60and 100 from becoming affixed together by air pressure as could occur ifthe contact area 190 was a large, closely fitting surface. Typically theair gap 290 will occupy more than 80% of the contact opening 195.

Ideally, the doors 60 and 100 should fit together so that perimeters 280and 285 form one continuous surface. Therefore, joggle 295 whereperimeters 280 and 285 meet should be kept as small as possible (e.g.,less than 0.010-0.020 inch) since particles on the joggle 295 will bebrought within the clean spaces 10 and 90 when the interface 110 isopened. Some particles may be present on the perimeters 280 and 285 so aparticle gutter 297 is provided on door 60 to catch any particles whichmight roll down the perimeters 280 and 285 when the interface 110 isopened. Alternatively, particle gutter 297 can be omitted to permit anyparticles from the perimeters 280 and 285 to settle all the way to thebottom of the canopy 10.

FIG. 6 shows a SMIF box storage unit 300. The box storage unit 300 isbasically an open rack for storing cassette boxes 90.

FIG. 7 shows a cassette storage unit 320 for storing cassettes 80holding IC wafers. The cassette storage unit 320 is a desiccator boxwith a canopy 10, port 20, and manipulator 30 added to it. The cassettestorage unit 320 will typically function as a cassette processingbuffer.

Initial cassette entry into the SMIF system occurs through the systeminterlock 330 as shown in FIG. 8. This is typically a four-foot wideglove box with an access chamber 340 at one end and a SMIF port 20 atthe other end. The complex movements required to transfer wafers from anew wafer package 345 into a cassette (not shown) necessitates the useof gloves 350 rather than mechanisms. Cassettes 80 and wafers enter andleave the SMIF system through the access chamber 340. Note that sincethe internal pressure of the system interlock 330 can change abruptly ashuman arms are thrust in and out of the gloves 350, it is necessary thatthe system interlock 330 be tightly constructed to prevent the intrusionof outside unfiltered air and it is also necessary to utilize an airfiltration unit 355 on the system interlock 330. The air filtration unit355 can contain both a conventional forced air filter and/or a particlecollector such as an electrostatic precipitator. Although generally lessdesirable from a particle contamination standpoint than using mechanicalmanipulators 30 on the canopy 10 as shown in FIG. 1, gloves 350 could beused to provide further flexibility of motion within canopy 10. Suchgloves 350 are especially useful to provide maintenance within canopy 10during periods when no IC wafers are present which can be contaminatedby the intrusion of outside unfiltered air caused by use of the gloves350. Filtration units 355 could also be used on the canopy 10 duringsuch maintenance periods to remove any particles which may haveintruded.

Because ICs are transported in their own closed containers and handlingis done by mechanical arms it is also possible to fully automate the ICproduction facility by the use of stationary or mobile robots which usecomputer controlled robotic manipulators coupled to the SMIF components.Whether handling is done manually or automatically, by combining theSMIF components with conventional IC processing equipment the ICfabrication area can for the first time be constructed without the needof a conventional clean room environment, while at the same timeimproving IC cleanliness.

We claim:
 1. An interface between first and second containers comprising:alignment means for orienting the first container in a fixed position relative to the second container; a first door for independently sealing the first container; a second door for independently sealing the second container; said first and second doors each having a mating outer surface of substantially equal exterior dimensions, so that substantially all contamination which has accumulated on the exterior surface of the doors when the containers are separated will be trapped between said doors when the containers are positioned together with said alignment means; and elevator means coupled to said doors for transporting said doors into said containers as a single unit while said doors are coupled together at their mating outer surfaces and said doors are held together substantially only by gravity.
 2. An interface as in claim 1 wherein said door mating outer surfaces contact substantially only in a region within a limited distance around the entire outer perimeters of said doors, so that the surface area of contact is small relative to the total surface areas of the doors.
 3. An interface as in claim 2 wherein the surface area of contact is less than 20% of the total surface areas of the doors.
 4. An interface as in claim 1 wherein the trapped contamination comprises particulate matter. 